Changes

## "Movement and button presses of the mouse must not cause the window to lose focus"

## "Synthetic mouse events created by application script act the same regardless of lock state"

## "[Upon unlock() t]he system mouse cursor must be displayed again and positioned at the same location that it was when mouse lock was entered (the same location that is reported in screenX/Y when the mouse is locked)"

## "When mouse lock is lost or disabled for any reason user agents must fire an event named mouselocklost with its bubble attribute set to true to the mouse lock target element"